An integrated system for telescope control using FPGA(s)

Abstract

Astronomical radio interferometers typically consist of an array of antennas, widely separated and connected using a transmission line. Signals recorded from each antenna are sent to a back-end where they are digitised, channelised and superposed, giving rise to constructive / destructive interference depending on their phase difference. This technique of interferometry is called aperture synthesis and it results in a combined telescope with a resolution equivalent to that of a single antenna with a diameter equal to the spacing of the antennas furthest apart in the array. When we consider a radio signal from a celestial source, incident on two antennas separated by a distance, the antennas receive the radio signal with a time difference, causing the signals to be out of phase. In order to achieve power amplification, the recorded signals must be phased using a technique called beamforming. A beamformer, has the added capability of steering the beam of a radio telescope using constructive / destructive interference. The aim of this project was to design and implement an integrated control system (ICS) for the digital steering of beams in a radio telescope. The system design was based on the PAPER F-engine and implemented on the ROACH2 FPGA board. A beamformer module was designed using the CASPER XPS tool-flow to be capable of continually steering beams in the sky, whilst monitoring the behaviour of a phased array system to ensure that the beams are continually tracking a source.